The organization and control of expression of immunoglobulin genes in immune and nonimmune cells, and the role of immunoglobulins in T lymphocytes will be investigated. DNA representing the complete Lambda gene locus will be isolated from a cloned library of mouse "germline" DNA and the organization of Lambda genes will be determined by restriction mapping, electron microscopy and DNA sequencing. The organization and structure of normal "germline" Lambda genes will be compared to Lambda genes in cloned DNA derived from myelomas which express Lambda gens and from "germline" DNA of SJL mice. The latter have a genetic defect in Lambda gene expression linked to the Lambda locus. The control of immunoglobulin gene (Lambda, Kappa, H) expression will be studied in T lymphocytes and B lymphocytes of different developmental stages (pre B cell to plasma cell) by determining the sensitivity of the respective genes to digestion by DNase I. Increased sensitivity to DNase I is associated with an altered chromatin state in potentially active compared with inactive genes: current work in our laboratory has shown that all CKappa, but not all VKappa gens, are DNase I sensitive in myelomas which produce Kappa chains. The structure of the antigen reactive moiety of T lymphocytes will be studied: T cell lines will be produced which express a particular variable region gene and the organization of this gene and the structure of the mRNA coded from it will be determined. The studies proposed in this application deal with some of the major questions in immunology. The solution of these questions will probably influence the elucidation of certain diseases which seem to be related to defects in B and/or T cell regulation, like autoimmunities, hypersensitivities, immunodeficiencies and may be cancer. Also, the immune system represents an interesting (special?) case of gene regulation, i.e. information obtained here will feed back on biology in general.